The success, albeit delayed, of the Hubble Space Telescope has encouraged and inspired work directed to other space-based (such as earth-orbiting) astronomical observatory platforms. Depending on the type of data to be gathered, a telescope with a large diameter primary optic, such as a 6 to 8 meter diameter (or larger) reflector would be particularly useful for astronomical observations. A number of approaches directed to achieving such an observatory have centered around the concept of a visible to infrared, 6 to 8 meter diameter space-based scientific observatory sometimes referred to as the Next Generation Space Telescope (NGST).
Realization of a large diameter space-based astronomical observatory would involve overcoming a number of problems. Launching such an instrument into orbit means that the payload mass of the observatory must be maintained as low as feasible. In some lightweight designs, optical or other components are not self-supporting in an earth gravity environment and thus cannot be fully or easily tested on earth prior to launch.
The volume and shape of payloads or cargo bays available on current launch vehicles places constraints on the size and shape of such an observatory. In general, a design providing a monolithic primary mirror would present significant manufacturing risks and, particularly in combination with a fixed secondary mirror support structure or truss, would require a launch vehicle with a very large interior volume.
Designs which envision a deployable observatory present another set of potential problems. Interest in a large-diameter primary optic typically means that the primary optic would be one of the components which was deployable, particularly if it is desired to avoid the cost of modifying or redesigning launch vehicles. However, in order to achieve a desired optical quality, such a deployable primary optic must, at least in some designs, have its components aligned to a very high degree of precision, such as within about 10 nanometers. Experience dictates that some account should be taken of the possibility of malfunction or failure in the deployment (or other systems). Accordingly, it would be useful to provide a deployable telescope which would avoid the need for a large number of high-precision alignments of components and which would reduce the potential for loss of function in the event of full or partial deployment failure.
These problems are multiplied as the number of components that must be repositioned in order to effect full deployment increases. Accordingly, it would be useful to provide a deployable space-based telescope which reduces or minimizes the number of components which must be moved to achieve full deployment, particularly the number of deployable optical elements.